During spermatogenesis in the rat testis, histones and nonhistone chromatin proteins are replaced by at least three spermatidal basic nuclear proteins. We propose to isolate the mRNA(s) coding for one or more of these proteins. We have isolated rat testis polysomal RNA and postribosomal supernatant RNA in yields of 1.5 and 0.34 mg per testis respectively. Both RNA samples are biologically active in a cell-free protein synthesis system from wheat germ. When 1 microgram of RNA is used in a 0.1 ml reaction for 60 min., 3H Leucine is incorporated into acid-insoluble material at levels of 6 and 3 pmoles for polysomal RNA and supernatant RNA respectively. The RNA samples are being fractionated by sucrose gradient centrifugation and oligo (dT) cellulose chromatography. We are combining several testis cell purification techniques such as hydroxyurea treatment, X-irradiation, centrifugal elutriation, and centrifugation in Percoll (Pharmacia) gradients in order to obtain at least 1 x 10 to the 8th power of each of the following cell types in greater than 90% purity: elongated spermatids, round spermatids, and pachytene primary spermatocytes. These viable cells will be used to identify the cellular locations of specific mRNA(s).